In terms of your deployed Apps here is some information to help you decide what iOS versions you want to support ....
• Some iOS stats state that 4.x is installed on < 10% of devices.
• iPhone 3G is limited to iOS 4.2.1.
• iPhone 3GS, 4, 4S and 5 can upgrade to iOS 5.x or iOS 6.x.
• iPad 1 is limited to iOS 5.1.1.
• iPad 2 and 3 (aka: New) can upgrade to iOS 5.x or iOS 6.x.
http://stackoverflow.com/questions/9751 ... rt-ios-5-0